1. Field of the Invention
The present invention relates to an apparatus that detects a combustion state of an internal combustion engine, and more particularly, to an apparatus that detects abnormal combustion.
2. Background Art
Problems of environmental conservation and fuel depletion are being raised in recent years and it is a big issue in the auto industry to cope with these problems. Under these circumstances, a variety of techniques to increase efficiency of an internal combustion engine to the maximum extent possible have been developed. With these techniques, however, abnormal combustion occurs more frequently and there arise problems that the internal combustion engine is damaged and durability and marketability are reduced.
As an apparatus capable of detecting abnormal combustion, an apparatus described in JP-A-2009-57940 is proposed. This apparatus detects the occurrence of pre-ignition and strength thereof according to generation end timing of an ion current, and it is configured to calculate the strength of pre-ignition in accordance with a relational expression of the generation end timing of an ion current and the strength of pre-ignition found empirically in advance.
The apparatus described in the cited reference calculates the strength of pre-ignition in accordance with the relational expression of the generation end timing of an ion current and the strength of pre-ignition found empirically in advance. The generation end timing of an ion current, however, is known to vary with an engine speed of an internal combustion engine, a load, an air-fuel ratio, spark timing, components of fuel, specifications of a detection probe, and other various environmental conditions. Because an actual vehicle is not provided with practical means for detecting the components of fuel and the specification of the detection probe, it is impossible to change a threshold value with which to determine the occurrence of pre-ignition by taking such variance-causing factors into account. This incapability therefore poses a problem that the detection accuracy is deteriorated.
In addition, in order to set the threshold value, albeit unreasonably at some sacrifice of detection, enormous man hours are necessary for examination. Further, there is a problem that more man hours are necessary to adjust the environmental conditions (in particular, temperature and pressure), an amount and timing of fuel injection, spark timing, and so forth in compensating for differences deriving from places of destination of a vehicle incorporating the internal combustion engine, that is, to perform matching again using different engine calibrations.